The present invention relates to a method of optically detecting the position of an object and the apparatus therefor.
An optical position detection apparatus has been known as shown in FIG. 1(A), said apparatus comprising a detection panel constituted by plural pairs of light emitting devices and photodetectors, each pair of said light emitting device 1 and said photodetector 2 being spaced from each other by a specified distance, and capable of detecting the position of an object 3 on said panel by sequentially moving a pair of said devices. Furthermore, in order to solve the problem of a possible variation in the light reception value of each light emitting device possibly arising even when no light emitted from said light emitting devices 1 toward the corresponding photodetectors is interrupted by an object, a detection apparatus has been developed by the applicant of the present invention and filed for as patent application on Jun. 29, 1990, as application Ser. No. 07/154,559, the detection apparatus being provided with a function of adjusting to be constant the light reception values of the respective photodetectors when there is no light being interrupted by a target. The adjusting function of said detection apparatus is also incorporated in an embodiment of the present invention. In short, when there is no light interrupted by an object and the light emitting drive value for the respective light emitting devices is equal, any variation in the respective light reception value of the respective light emitting devices is detected, the individual light emitting drive value necessary for driving each light emitting device is computed in accordance with the detected respective light reception value and stored, and the detected variation of the light reception values is adjusted in accordance with the individual light emitting drive value so that the respective light reception value becomes uniform when there is no light being interrupted by an object.
FIG. 1(B) illustrates the presence and absence of light interruption by an object detected at the respective photodetectors (light interruption being caused by the presence of "touch" at the panel) in the optical position detection apparatus incorporating the adjustment function as above described. The abscissa designates the corrdinate of the respective photodetectors and the ordinate indicates the results of optical detection which can be indicated as a presence or absence of the light interruption by an object as the result of comparing the respectively adjusted light reception value with the reference level which is set to determine a presence or absence of light interruption.
According to the conventional method and apparatus of optically detecting a position, the light reception value of the respective photodetectors is detected as a signal to indicate it to be either above or below the reference level, or presence or absence of an object regardless of said adjusting function. In this sense, the accuracy for detecting the position of an object had to be attained only by the resolution equivalent to half of the light corresponding a pitch between photodetectors. For example, in FIG. 1(B), since the abscissa 4 and 5 are detected to indicate the presence of light interruption, the position of an object is detected as the abscissa of (4+5)/2=4.5. In order to solve this problem, a method and an apparatus of optically detecting a position which is capable of detecting the position of an object with an accuracy of more than 1/2 of the pitch (or length) between adjacent photodetectors has been demanded.
Accordingly, an object of the present invention is to provide a method and an apparatus of optically detecting a position which is capable of improving the accuracy of detecting the position of an object at least more than 1/2 pitch.